1. Field of the Invention
The present invention relates to a keyboard device for use in computers and the like, which has a pointing device using strain gauges incorporated therein.
2. Description of the Related Art
A conventional keyboard device will be described with reference to FIGS. 4 and 5. The conventional keyboard device comprises a membrane switch S2, a pointing device P2 incorporated in the membrane switch S2, and a mounting plate T2 made of metal for mounting and supporting the membrane switch S2 and the pointing device P2.
The pointing device P2 comprises, as shown in FIG. 5, a mounting member 21 formed of a metal plate, a control member 22 made of synthetic resin, mounted on the mounting member 21, and having an operating portion 22a and a plurality of strain gauges (not shown), a long flexible substrate 23 attached to the control member 22 at one end and made of polyester resin, and connection conductors 24 formed on the flexible substrate 23 so as to electrically connect the strain gauges to the outside.
The flexible substrate 23 includes a base portion 23a a long extension 23b. The base portion 23a is provided with connection conductors 24 to be connected to the strain gauges in the control member 22, and the extension 23b is provided with connection conductors 24 for leading the above connection conductors 24 connected to the strain gauges to the end of the extension 23b. A resist 25 made of an insulating material is applied to the surface of the flexible substrate 23 so as to cover and insulate the connection conductors 24, excluding the connection conductors 24 at the end of the extension 23b. 
In the operation of such a pointing device P2, the operating portion 22a of the control member 22 is tilted in the X1- or X2 direction to change the resistances of the strain gauges, thereby controlling the horizontal movement of a cursor. Furthermore, the operating portion 22a is tilted in the Y1- or Y2-direction to change the resistances of the strain gauges, thereby controlling the vertical movement of the cursor.
That is, the changes in resistance of the strain gauges are detected as changes in voltage, and a computer reads the voltage changes and controls the cursor so that the cursor moves horizontally or vertically in response to the movement of the operating portion 22a in the X1- and X2-directions, or in the Y1- and Y2-directions.
The membranes switch S2 is formed of a polyester resin and includes a rectangular lower film substrate 26, a rectangular upper film substrate 27 placed at a predetermined distance from the lower film substrate 26 with a spacer (not shown) therebetween, and a rectangular leader portion 28 formed integrally with the lower film substrate 26 and protruding therefrom.
A plurality of contact portions (not shown) and a layout conductor (not shown) connected to the contact portions are formed on the opposing surfaces of the lower and upper film substrates 26 and 27. The layout conductor is connected to membrane switch terminal portions 29 formed on the leader portion 28.
When a pressure portion 27a of the upper film substrate 27 is pressed, the upper film substrate 27 is bent, and a contact portion thereof contacts a corresponding contact portion of the lower film substrate 26, whereby a signal is led out to the membrane switch terminal portions 29 via the layout conductor.
The lower and upper film substrates 26 and 27 have holes 26b and 27b for holding the pointing device P2 therein. The leader portion 28 has two cut portions 28a. 
The pointing device P2 is placed inside the holes 26a and 27a so that the extension 23b of the flexible substrate 23 is disposed in no contact with the contact portions between the lower film substrate 26 and the upper film substrate 27 without hindrance (shown by a two-dot chain line in FIG. 4). Moreover, the end of the extension 23b is drawn out through the two cut portions 28a so as to support the extension 23b, and the connection conductors 24 and the membrane switch terminal portions 29 are arranged in parallel.
The membrane switch S2 and the pointing device P2 thus combined are fixed on the mounting plate T2 by an appropriate means, such as caulking or bonding, thereby constructing the keyboard device.
The membrane switch terminal portions 29 and the connection conductors 24 in such a keyboard device are connected to an electronic device, such as a computer, and signals from the membranes switch S2 and the pointing device P2 are input to the electronic device.
The conventional keyboard device requires the long flexible substrate 23 to lead out signals from the pointing device P2 to the position of the membrane switch terminal portions 29, which raises material cost.
Since the long flexible substrate 23 also has a complicated shape in order to avoid the contact portions, the process of preparing the material is not simple, which further raises the costs.
The extension 23b of the flexible substrate 23 needs to be passed through and drawn out of the cut portions 28a of the leader portion 28 for the purpose of mounting and support, which impairs assembly work efficiency and raises the costs.
In view of the above problems, an object of the present invention is to provide a keyboard device that achieves a low material cost and a simple process of preparing the material.
In order to achieve the above object, according to an aspect of the present invention, there is provided a keyboard device including: a membrane switch having two upper and lower film substrates with a plurality of contact portions 14a, and a leader portion formed integrally with the film substrates; and a pointing device incorporated in the area of the membrane switch and having a strain gauge and a flexible substrate for electrically connecting the strain gauge to the outside, wherein the leader portion is provided with a switch terminal portion and a pointing device terminal portion, the film substrates are provided with a lead-out conductor to be led out to the pointing device terminal portion, the flexible substrate is provided with a connection conductor, and the connection conductor is connected to the lead-out conductor adjacent to the pointing device.
This makes it possible to make the flexible substrate substantially shorter than before, and to thereby provide a low-cost keyboard device that achieves a low material cost and a simple process of preparing the material.
Furthermore, there is no need to pass the flexible substrate through the cut portions of the leader portion, as is different from the conventional art. Therefore, it is possible to provide a low-cost keyboard device that achieves high productivity.
Preferably, the flexible substrate includes a base portion on which the strain gauge is disposed, and an extension formed integrally with the base portion and having the connection conductor from the strain gauge formed thereon.
In this case, it is easy to connect and construct the strain gauge and the connection conductor, and to thereby provide a keyboard device that achieves high productivity.
Preferably, the pointing device includes a control member attached to the base portion of the flexible substrate and for operating the strain gauge, and a mounting member formed of a metal plate for mounting the control member thereon. The connection conductor is connected to the lead-out conductor within the surface area of the control member or the mounting member.
In this case, it is possible to establish a substantially short length of connection between the pointing device and the membrane switch, and to thereby provide a low-cost keyboard device that achieves high productivity.
Preferably, the film substrates are made of polyester resin, and the flexible substrate is made of polyimide resin.
Since the strain gauge is formed on the flexible substrate of polyimide resin having high resistance to heat, changes in resistance are accurate in the pointing device. Moreover, since the members are small, it is possible to provide a low-cost input device.
Further objects, features, and advantages of the present invention will be apparent from the following description of the preferred embodiments with reference to the attached drawings.